Feb
17
Written by:
Tom
2/17/2010 9:11 PM
Peter Conway sends us another look into the Systems Program. This month: diesels as far as the eye can see!
Systems Program report, by Peter J Conway
Diesel Engines
This month we cover Diesel Engines in class and get our hands dirty in the lab. Students learn the principal requirements of diesel engine operation: Air, fuel, combustion. “The tripod” is used as an analogy to remember this basic principle. Lecture covers the history and development of the diesel engine over the past 100 years. Improvements in metallurgy and the advancements in closer tooling tolerances have increased the thermal efficiency and power to weight ratio of the modern diesel engine core. Additional improvements to the air side of things such as turbo chargers, superchargers, inner coolers, and after coolers have dramatically increased output. On the fuel side we explore electronically controlled fuel injection that has exponentially enhanced fuel economy. Maintenance schedules are reviewed and proper techniques for servicing are addressed. Students are paired into teams of two and given engine assignments. Each team has a different engine to inspect, clean, and overhaul.
[Ed. Note: Be careful when choosing a work partner. Some just lie around and make you do all the work. ]
Lab
Before we start our engines the “starter circuit” is drawn out and our engine monitoring gauges are detailed in a wire diagram. The wire diagram shows the connections that the wires will make on the instrument panel
and where the wires will go to on the engine. Monitoring sensors that we will be installing are engine water temperature, battery volts and oil pressure.
On our system we will install a momentary preheat switch, when activated, will also power the start momentary switch. Power to the daisy chained switches will be drawn from the ignition. Proper installation allows for future service by including a bend called a ‘service loop’ in the wire run. Wire gauge is calculated for each circuit based on amp requirements and the length of run. We will use 2/0, pronounced ‘two-oht’ for our heavy gauge DC.
A battery start switch is installed. ABYC standards indicate that any starter circuit over 800 Cold Cranking Amps requires a battery switch. From the battery, heavy DC wire is run to the start switch and then to the solenoid on the starter.
A start circuit is designed with a remote solenoid.
Due to the high amp draw of the starter motor we will use the remote solenoid to switch the heavy DC circuit on/off This allows us to use a smaller gauge wire to control the solenoid and switch the starter circuit on and off with lower amperage. The circuit is activated by the ignition.
A close inspection of our assigned engine reveals that there is a gasket problem on our closed water circuit pump. This pump circulates a 50/50 coolant + water mixture throughout the engine block to maintain optimum operating temperature. We remove our pump
and discard the old gasket material.
A new gasket is traced out and cut from loose gasket stock. While replacing this gasket we find that the pump has a hole on the housing about a centimeter in diameter. To repair it we clean out the hole with a Dremel Tool and mix up some Marine Tex to patch it. We let the repair cure overnight.
The patch is sanded smooth and flat the next day and is ready for reassembly.
Some engines in the shop are fit with electronic stop solenoids. Others are equipped with a makeshift cable pull to simulate a fuel shut off. Both serve the same function but achieve the result in dramatically different ways. Our engine does not have the electronic stop solenoid so my teammate Lenny Anderson goes to work in the shop to find one. A few minutes later Lenny turns up a stop solenoid from another Westerbeke that is currently not running and we are in business. We retro fit our engine with a bracket made from loose 90 degree angle aluminum stock from the recycled materials pile. Our repurposed stop solenoid holds the fuel lever in the on position when the circuit is activated.
The normally closed stop solenoid moves a small ram in and out.
When the momentary stop switch is depressed on the instrument panel the solenoid becomes disengaged and the ram retracts, thus shutting off the fuel to the engine.
Instrument panels on mid size recreational vessels will occasionally provide the operator with engine monitoring gauges and alarms. For our instrument panel we added a low oil pressure alarm and flashing LED’s.
Upon start up this circuit is normally closed and the alarm is sounding when the ignition is switched to the on position. Once the engine is started the oil pressure will build and the normally closed oil pressure switch will open the circuit. The alarm will turn off and the lights stop flashing. When the engine is shutdown or there is a loss of oil pressure the alarm will sound again and the lights will flash.
Gentlemen, start your engines!
Oil changes are a necessary part of properly maintaining your diesel engine. Students are instructed on proper maintenance schedules and how to keep detailed service records. Liability claims are discussed and the ramifications of poor record keeping explained.
Students replace primary and secondary fuel filters and then purge the air from the system by bleeding the fuel line at the secondary fuel filter. The engine is then started to check that the fuel lines are properly bleed out. If needed the injector pump and the injectors are purged as well. Air bubbles will cause erratic engine operation especially at low RPM. Students rotate engines and attempt to bleed each others fuel systems to get some hands on experience.
To properly change the engine oil we will run up the engine to desired operating temperature 140-160F (60-71C). Hot oil has a lower viscosity; therefore it will drain down easier out of the engine. Boats unfortunately are not as easy to change the oil in as your car is. We cannot simply drive into the nearest EZ-Lube and pull the plug out. Typically it is very difficult to find an oil pan that you can just pull the plug on. By warming the oil we can use an evacuation pump to suck the oil out of the engine sump through the dip stick with a tube. You can install an electric sump pump to facilitate this procedure if desired. Some larger engines will incorporate an oil change system that removes and replaces oil on board in a closed system. For our Lab we will use the evacuation pump. Evacuation pumps can be either electric or hand operated. Either one works well and both are equally as messy. Always properly recycle used oil. Never dump used oil overboard or simply let it drain into the bilge to be pumped out. Students determine proper filter element and change out oil filter as well. The engine is then refilled with the proper oil as called out by the engine manufacturer. Note: Oil will fill the filter once the engine has been started. Recheck the oil level after the engine has run for a few minutes. Then top off. It is good practice to collect a sample of the used engine oil and send it out to a lab for analysis. Oil analysis is a good way to determine your engines state of health. This procedure can save you costly repairs in the future and provide you with useful feedback regarding your maintenance routine.
Diagnostics
Today we have several tests that a diesel technician can perform to determine the source of an engine problem. We will learn three typical procedures that are employed today. They are the compression test, pop test, and leak down test. (Note: We will look at electronic diagnostic tools in the next section.)
The compression test is performed by students to check the cylinder for proper compression pressure. We remove a glow plug from one of the cylinders in our engine and insert an adapter to fasten the pressure gauge. Then we crank the engine over a couple of times while holding the engine shut down lever. Check the pressure on the gauge with manufacturer recommendations.
Record findings and compare with the remaining cylinders. Rings, valves, gaskets, and liners can all wear out over time and leak air out of the cylinder combustion chamber.
The ‘Pop’ test is a way to check fuel injectors for proper function. Microscopic contaminates in the fuel can block injectors and can cause irregular spray patterns. Malfunctioning injectors will not atomize fuel properly in the cylinder. This will lead to increased engine wear and poor engine operation. If left unchecked fuel will dissolve the barrier of lubricating oil that protects the cylinder liners from wear and your engine will eventually seize. We remove each injector from the engine and pop test it with a device that simulates a fuel pump. Spray patterns are visually inspected and the pressure at which the injector “pops” at is recorded.
Lastly, the leak down test is a diagnostic tool we use to determine the performance of the engines gaskets, seals, and rings. We bring each cylinder to TDC (top dead center) and fill the cylinder with 90psi of compressed air. In our engine we do this using the glow plug port again. An adapter is threaded into the engine block and an air compressor is attached.
A little air leaks out and then we record the pressure the cylinder holds at.
These numbers are checked against a chart and the percentage leak is recorded for each cylinder. Gaskets are made for engines that have unacceptable leakage.
Valves are another area where leaks are found. Instructor John Stier demonstrates how to lap valves that are not seated well. Valve clearance is checked by rotating the crank until the first cylinder is aligned at top dead center or TDC.
When in this position the intake valve and the exhaust valve are both closed. The cam shaft rotates, pushing on the push rods that in turn move the rockers that open and close these valves. Students adjust the clearance between these rockers and the valves.
We use a tool called a feeler gauge to set the clearance to manufacturer’s recommendations. Tolerances are exact to the thousandths (.001) of an inch.
Engines are disassembled in every corner of the shop. Students work in teams to service any areas that require attention.
Belts, hoses, clamps, engine mounts, alternators, heat exchangers,
you name it, are inspected. The parts washer is hard at work cleaning up various engine components and water is boiling to test thermostats in the galley.
Students are given several take home assignments/challenges. We are asked to calculate the ventilation requirements for an engine of our choice and tasked to create an intake & exhaust system that will move enough air through the engine room space. Students also prepare an hourly maintenance summary for their assigned engines.
Shop Talk
ABYC Diesel certification exam is scheduled for Friday Feb. 12,2010
Work continues on Renegade every morning before class and almost every evening after.
Students are making solid progress on the systems overhaul/ restoration. Each component that needs attention is assigned to a team and the teams rotate time on the boat.
The engine has been removed and the wiring has been replaced.
Sea cocks and thru-hulls are inspected and replaced.
A new DC power distribution system is designed and installed.
Proper navigational lights are permanently installed. Paint has been removed from the deck and the finishing touches are being made to the new instrument panel.
Pictures tell a thousand words.
Field Trips
Providence Boat Show
Students visit Providence to check out the newest trends in the marine industry. IYRS president Terry Nathan is invited to speak at the Rhode Island Marine Trades Round Table panel discussion on the future of the boating industry in the state of Rhode Island.
Cummins North EastIYRS students travel to Massachusetts and met with Cummins lead technician trainer Brian Coleman. We are given a brief tour of the facility and then a short training seminar on electronic fuel injection.
Students have a chance to ask questions and discuss how to get started in the industry.
H & H PropellerWe travel to Salem, MA to visit H&H Propeller. Students met with owner Robert Pelletier and Sales Manager Jeff Boryszewski. We are given an ‘all access tour’ of their facility and machine shop.
Time honored and traditional propeller repair methods are explained and demonstrated by H&H employees. Students are given a personalized propeller selection seminar and various propeller terminologies are explained in great detail.
[Ed. Note: Propeller term of the day; "Chowdered"]
Robert walks our class through the advances in propeller construction and repair methods. From the trusty mallet to the MRI computer aided balancing machines, tuning a propeller is a craft that you must get a feel for.
We are shown the machine shop and met with Ernie the Shop Foreman. Ernie walks us through the process of straightening a shaft.
H&H Propeller can make just about any propeller shaft you can think of. Ernie demonstrates how he does this with large robotic CNC machines that have big price tags.
IYRS is given the test stock propeller shaft that we made in the demonstration as a gift.
Renegades propeller and shaft will be balanced and tuned by H&H as part of our restoration project.
Brewers BoatworksIYRS students once again visit another Brewer Yard for an afternoon outing. Students met with President Jay “Skip” Helme Jr. and were shown the Newport facility.
Interesting point to mention is the work space in the service area is heated with recycled motor oil from winter service lay up. Work continues indoors in the heated areas throughout the winter. Various notable projects that were undertaken by the Brewer Team were explained and students were shown the ‘Spray Room’ where a couple of yachts were being re-painted. Service Manager Randy Both continued the tour and explained how technicians service outboard engines for winter storage.
Computer based diagnostic software is demonstrated to check engine state of health. Outboard mechanic Steve Bradfield shows students the inner workings of the modern four-stroke outboard.
You don’t see the inside of these engines everyday. Testing is done in a tank to simulate operational conditions.
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